radiocarbon Carbon Isotopes (12C, 13C, 14C) Background 14C is a radioactive isotope of carbon. It was discovered in 1934 by Grosse as an unknown activity in the mineral endialyte. In the same year, Kurie (Yale) exposed nitrogen to fast neutrons and observed long tracks in a bubble chamber. He had produced 14C. It was in atmospheric CO2 by Libby in 1946. He determined the half life to be 5568 years. This half life has later been re-determined by Godwin. The new half life is 5730 years. Libby recognized that due to its occurrence in natural materials, 14C can be used as a dating tool for materials that contain carbon compounds derived from atmospheric CO2 either by simple mixing processes or by carbon exchange. The mean life time of roughly 8000 years is ideal for dating of reservoirs that are a few decades to a few ten thousand yeas old.

For groundwater, this means that 14C dating can be applied to aquifers that contain water formed during periods that reach well into the past glacial time. 14C is a widely used tool to establish chronologies for groundwater flow systems and climate records for the Holocene and Pleistocene. It is considered to be the most important tool for age dating of ‘old’ groundwater. The challenge in 14C dating of groundwater is the determination of the initial 14C content of groundwater at the time of recharge, i.e., at the time when groundwater is isolated from exchange with the soil air and moves away from the water table. There is also a stable isotope of carbon, 13C. This isotope is important in that it allows us to correct for carbon isotope fractionation in nature and during analytical procedures.

Abundance of carbon isotopes in nature 12C 1.11 % ~10-12 13C measurements are reported in the d13C notation relative to a standard (PDB, or the newer VPDB standard, considered identical to PDB) Isotope ratios are typically measured by mass spectrometry d13C values cover a wide range in nature ( Fig ) influenced by fractionation processes analogue to what we discussed in the water isotope section 14C activities are referred to an international standard, known as as 'modern carbon' Natural 14C production 14C is mainly produced by interaction of cosmic ray derived secondary neutrons with 14N in the atmosphere.

14N (n,p) 14C 14C can also be produced by the following reaction: 13C(d,p)14C d: deuterium or 2H the production rate is 2.4 ± 0.2 atoms (cm2 sec)-1 The production rate has not been constant over time, comparison with tree ring chronologies and corals have shown variations in the production rate which result in an offset between calendar and 14C ages of thousands of years ( Fig ) ( Fig ) Radioactive decay 14C decays by b- decay with a maximum energy of 0.158 MeV. 146C -> 147N+ e- + anti-neutrino+ Q Its half life t is 5730 years, i.e., somewhat larger than the half life determined by Libby (5568 ys). Differnt fields tend to use different half lifes. Natural global inventory The global inventory of natural 14C is about 75 tons. The specific activity in pre-industrial times was 13.56 dpm (gC)-1. dpm stands for decay per minute.

Anthropogenic 14C production The main source of anthropogenic 14C is so-called ‘bomb’ 14C, i.e., 14C produced during atmospheric testing of nuclear weapons. At the peak of surface testing of nuclear devices in 1963, the atmospheric 14C activity had reached about twice that of natural 14C ( Fig ). The bomb 14C has been produced by interaction of atmospheric nitrogen with the high neutron flux from the explosion of nuclear devices (mainly thermonuclear devices). Local increases in atmospheric 14C have been observed in the vicinity of nuclear power plants. Before bomb production began, 14C (and 13C) dropped due to anthopogenic emisssions of fossil carbon (Suess effect, Fig ) Notation The notation of 14C activities is discussed in detail in Stuiver and Pollach (Radiocarbon, 19, 355-365, 1977). In short, 14C is calibrated against an NBS (National Bureau of Standards) oxalic acid standard.

The internationally accepted radiocarbon dating reference is 95% of the activity, in 1950 AD, of the NBS oxalic acid normalized to d13C of –19.3‰ with respect to PDB. The factor of 0.95 adjusts the oxalic acid to the activity of wood from 1840 to 1860 (‘pre-industrial’). Results are reported in pmC (% modern carbon). A0N = 0.95 AOX [1 – 2.3(d13C + 19.3)/1000] AON: 14C activity of oxalic acid normalized for 14C fractionation AOX: 14C activity of oxalic acid The d13C correction of 19‰ takes into account the fractionation of 14C during the combustion of oxalic acid. Generally radiocarbon concentrations of samples are normalized to a common d13C value of -25‰.

The fractionation for 14C is 2.3 times the fractionation for 13C and therefore the enrichment in 14C due to a factionation amounts to: 2.3(d13C + 25‰) For example if you have a sample with d13C = 1.5‰, and a 14C activity of 65pmc, the correction amounts to: 2.3(-25-1.5)/1000=-6.1%. The final radiocarbon value is the 65*0.939 = 61pmC. Groundwater: For groundwater studies, the pmc (percent modern carbon) notation is used.

pmc = (ASN/Aabs) 100% = ASN [AON e l(y-1950)]-1 100% ASN: activity of sample normalized for fractionation using d13C AON: 13C normalized activity of oxalic acid Aabs: Absolute 14C activity of the sample y: year of measurement of oxalic acid 14C dating Principle: In the atmosphere, 14C is incorporated into 14CO2 and takes part in the global carbon cycle. It is assimilated by plants. Except for isotope fractionation, 14C in living organic matter is the same as that in atmospheric CO2. After organic matter dies, the 14C concentration decreases due to radioactive decay. If there is no isotope exchange, radioactive decay is the only 14C sink and if the initial 14C activity is known, an age can be calculated from the measured 14C activity of a sample.

In groundwater applications typically DIC (dissolved inorganic carbon; DIC = CO2(aqueous) + HCO3- + CO32-) is extracted from the water a and its measured 14C activity is compared to the initial 14C activity. Determination of the initial 14C activity can be challenging and typically requires correction models that account for the carbon chemistry in the unsaturated and saturated soil zones. 14C(t) = 14C(t0) e-l (t-t0) D t = (t - t0) = -l-1 ln [14C(t)/14C(t0)] = T1/2 / ln2 {ln [+C(t0)/14C(t)]} l: radioactive decay constant of 14C: l = t-1; t : mean life time: t = T1/2/ln2 Initial 14C activity in groundwater See summary in Clark and Fritz (chapter 8) for details In short, the 14C activity of DIC (dissolved inorganic carbon) in groundwater is determined by the following factors: (Fig.

8.6 in Clark and Fritz): activity in soil CO2 (soil air and root respiration); activity » 100 pmc dissolution of carbonates (lime stone); activity » 0 pmc dissolution of carbonates can occur in the unsaturated soil zone (open system) or in the saturated soil zone (closed system). isotope exchange can lead to a decrease in 14C activity in addition to radioactive decay a variety of models can be used to estimate the initial 14C activity in groundwater. They include the very simple ‘Vogel’ model, several models that correct for carbon chemistry using chemical or 13C balances, and the complex NETPATH model by Plummer. The latter accounts for the chemical evolution of the groundwater along flowpaths.

14CO2 + H2O + CaCO3 --> Ca2+ + HCO3- completely open system: 14C activity: » 100 pmc completely closed system: 14C activity: » 50 pmc Chemical and isotopc evolution in recharge zone: ( Fig ) ( Fig ) Open and closed system conditions ‘real world’ systems are somewhere in between open and closed and the correction models mentioned above and described in Clark and Fritz (chapter 8) have to be applied. Measurement Technique: low-level b - counting using gas-filled proportional counters or AMS (Accelerator mass spectrometry) Water sample size: ca. 100 liters (low-level counting) or several hundred ml (AMS) Measurement precision: ± 0.2 to ± 1% (1-s error) for concentrations close to 100 pmc. This corresponds to an age resolution of about ± 16 to ± 40 years. Detection limit: <1% modern corresponding to ages of about 40000 years. There are many laboratories worldwide that can measure 14C routinely.

However, only few 14C laboratories have the capability to measure 14C at precisions of ± 0.2%. In groundwater studies the overall error is dominated by systematic errors and the analytical precision is not as critical as in oceanographic studies. Resources Radiocarbon Dating Key Concepts - Beta Analytic Radiocarbon Dating: An Introduction Willard Libby developed radiocarbon dating as a method to measure radioactivity. Carbon-14 is a weakly radioactive isotope of Carbon; also known as radiocarbon, it is an isotopic chronometer. Radiocarbon dating is only applicable to organic and some inorganic materials (not applicable to metals). Gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry are the three principal radiocarbon dating methods. Radiocarbon dating labs use Oxalic Acid I and Oxalic Acid II as modern standards. Radiocarbon measurements are reported as Conventional Radiocarbon Age. The impact of the radiocarbon dating technique on modern man has made it one of the most significant discoveries of the 20th century. No other scientific method has managed to revolutionize man’s understanding not only of his present but also of events that already happened thousands of years ago.

Archaeology and other human sciences use radiocarbon dating to prove or disprove theories. Over the years, carbon 14 dating has also found applications in geology, hydrology, geophysics, atmospheric science, oceanography, paleoclimatology, and even biomedicine. Radiocarbon Dating Pioneer American physical chemist Willard Libby led a team of scientists in the post World War II era to develop a method that measures radiocarbon activity. He is credited to be the first scientist to suggest that the unstable carbon isotope called radiocarbon or carbon 14 might exist in living matter. Mr. Libby and his team of scientists were able to publish a paper summarizing the first detection of radiocarbon in an organic sample. It was also Mr. Libby who first measured radiocarbon’s rate of decay and established 5568 years ± 30 years as the half-life. In 1960, Mr. Libby was awarded the Nobel Prize in Chemistry in recognition of his efforts to develop radiocarbon dating. Basic Principles of Carbon Dating Radiocarbon, or carbon 14, is an isotope of the element carbon that is unstable and weakly radioactive.

The stable isotopes are carbon 12 and carbon 13. Carbon 14 is continually being formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms. It is rapidly oxidized in air to form carbon dioxide and enters the global carbon cycle. Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes. When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay. Radiocarbon dating is essentially a method designed to measure residual radioactivity. By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known. It must be noted though that radiocarbon dating results indicate when the organism was alive but not when a material from that organism was used. Radiocarbon Datable Materials Not all materials can be radiocarbon dated. Most, if not all, organic compounds can be dated. Some inorganic matter, like a shell’s aragonite component, can also be dated as long as the mineral’s formation involved assimilation of carbon 14 in equilibrium with the atmosphere.

Samples that have been radiocarbon dated since the inception of the method include charcoal , wood , twigs, seeds , bones , shells , leather, peat , lake mud, soil , hair, pottery , pollen , wall paintings, corals, blood residues, fabrics , paper or parchment, resins, and water , among others. Physical and chemical pretreatments are done on these materials to remove possible contaminants before they are analyzed for their radiocarbon content. Principal Methods of Measuring Radiocarbon There are three principal techniques used to measure carbon 14 content of any given sample— gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry . Gas proportional counting is a conventional radiometric dating technique that counts the beta particles emitted by a given sample. Beta particles are products of radiocarbon decay. In this method, the carbon sample is first converted to carbon dioxide gas before measurement in gas proportional counters takes place. Liquid scintillation counting is another radiocarbon dating technique that was popular in the 1960s. In this method, the sample is in liquid form and a scintillator is added. This scintillator produces a flash of light when it interacts with a beta particle.

A vial with a sample is passed between two photomultipliers, and only when both devices register the flash of light that a count is made. Accelerator mass spectrometry (AMS) is a modern radiocarbon dating method that is considered to be the more efficient way to measure radiocarbon content of a sample. In this method, the carbon 14 content is directly measured relative to the carbon 12 and carbon 13 present. The method does not count beta particles but the number of carbon atoms present in the sample and the proportion of the isotopes. Radiocarbon Dating Standards The radiocarbon age of a certain sample of unknown age can be determined by measuring its carbon 14 content and comparing the result to the carbon 14 activity in modern and background samples. The principal modern standard used by radiocarbon dating labs was the Oxalic Acid I obtained from the National Institute of Standards and Technology in Maryland. This oxalic acid came from sugar beets in 1955. Around 95% of the radiocarbon activity of Oxalic Acid I is equal to the measured radiocarbon activity of the absolute radiocarbon standard—a wood in 1890 unaffected by fossil fuel effects.

When the stocks of Oxalic Acid I were almost fully consumed, another standard was made from a crop of 1977 French beet molasses. The new standard, Oxalic Acid II, was proven to have only a slight difference with Oxalic Acid I in terms of radiocarbon content. Over the years, other secondary radiocarbon standards have been made. Radiocarbon activity of materials in the background is also determined to remove its contribution from results obtained during a sample analysis. Background radiocarbon activity is measured, and the values obtained are deducted from the sample’s radiocarbon dating results. Background samples analyzed are usually geological in origin of infinite age such as coal, lignite, and limestone. Radiocarbon Dating Measurements A radiocarbon measurement is termed a conventional radiocarbon age (CRA).

The CRA conventions include (a) usage of the Libby half-life, (b) usage of Oxalic Acid I or II or any appropriate secondary standard as the modern radiocarbon standard, (c) correction for sample isotopic fractionation to a normalized or base value of -25.0 per mille relative to the ratio of carbon 12/carbon 13 in the carbonate standard VPDB – Cretaceous belemnite formation at Peedee in South Carolina, (d) zero BP (Before Present) is defined as AD 1950, and (e) the assumption that global radiocarbon levels are constant. Standard errors are also reported in a radiocarbon dating result , hence the “±” values. These values have been derived through statistical means. Carbon-14 Dating - Tracer: A substance, usually a labeled element, used to follow a complex sequence of biochemical reactions, as in an animal body, to locate diseased cells and tissues, to determine physical properties, etc. Half-life: The time required to for half the original nuclides to decay. Metabolic Processes: The chemical and physical processes continuously going on in living organisms and cells.

Isotopes: One of two or more atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. Carbon-14 Dating Radio-carbon dating is a method of obtaining age estimates on organic materials. The word "estimates" is used because there is a significant amount of uncertainty in these measurements. Each sample type has specific problems associated with its use for dating purposes, including contamination and special environmental effects. More information on the sources of error in carbon dating are presented at the bottom of this page. The method was developed immediately following World War II by Willard F. Libby and coworkers and has provided age determinations in archeology, geology, geophysics, and other branches of science. Radiocarbon dating estimates can be obtained on wood, charcoal, marine and freshwater shells, bone and antler, and peat and organic-bearing sediments. They can also be obtained from carbonate deposits such as tufa, calcite, marl, dissolved carbon dioxide, and carbonates in ocean, lake and groundwater sources. Carbon dioxide is distributed on a worldwide basis into various atmospheric, biospheric, and hydrospheric reservoirs on a time scale much shorter than its half-life.

Measurements have shown that in recent history, radiocarbon levels have remained relatively constant in most of the biosphere due to the metabolic processes in living organisms and the relatively rapid turnover of carbonates in surface ocean waters. However, changes in the atmosphere over the ages are a source of uncertainty in the measurements. Carbon (C) has three naturally occurring isotopes. Both C-12 and C-13 are stable, but C-14 decays by very weak beta decay to nitrogen-14 with a half-life of approximately 5,730 years. Naturally occurring radiocarbon is produced as a secondary effect of cosmic-ray bombardment of the upper atmosphere. Plants transpire to take in atmospheric carbon, which is the beginning of absorption of carbon into the food chain. Animals eat the plants and this action introduces carbon into their bodies. After the organism dies, carbon-14 continues to decay without being replaced. To measure the amount of radiocarbon left in a artifact, scientists burn a small piece to convert it into carbon dioxide gas. Radiation counters are used to detect the electrons given off by decaying C-14 as it turns into nitrogen.

The amount of C-14 is compared to the amount of C-12, the stable form of carbon, to determine how much radiocarbon has decayed, thereby dating the artifact. Exponential Decay Formula: A = A0* 2^(-t/k) Where "A" is the present amount of the radioactive isotope, "A0" is the original amount of the radioactive isotope that is measured in the same units as "A." The value "t" is the time it takes to reduce the original amount of the isotope to the present amount, and "k" is the half-life of the isotope, measured in the same units as "t." The applet allows you to choose the C-14 to C-12 ratio, then calculates the age of our skull from the formula above. Uncertainty in Carbon Dating As mentioned above, there is significant uncertainty in carbon dating. There are several variables that contribute to this uncertainty. First, as mentioned previously, the proportions of C-14 in the atmosphere in historic times is unknown.

The C-14:C-12 atmospheric ratio is known to vary over time and it is not at all certain that the curve is “well behaved.” Complicating things further, various plants have differing abilities to exclude significant proportions of the C-14 in their intake. This varies with environmental conditions as well. The varying rates at which C-14 is excluded in plants also means that the apparent age of a living animal may be affected by an animal's diet. An animal that ingested plants with relatively low C-14 proportions would be dated older than their true age. Attempts are often made to index C-14 proportions using samples of know age. While this may be useful to eliminate the uncertainty of atmospheric proportions of C-14, it does not compensate for local conditions such as which plant species are in the diet. The uncertainty in the measurement leads some to conclude that the method is far less predictive of age than is commonly supposed, especially for older samples.

Last updated on October 28, 2010 It's Elemental - The Element Carbon It's Elemental Melting Point: 3823 K (3550°C or 6422°F) Boiling Point: 4098 K (3825°C or 6917°F) Density: 2.2670 grams per cubic centimeter Phase at Room Temperature: Solid Element Classification: Non-metal Period Number: 2 Group Number: 14 Group Name: none What's in a name? From the Latin word for charcoal, carbo. Say what? Carbon is pronounced as KAR-ben. History and Uses: Carbon, the sixth most abundant element in the universe , has been known since ancient times. Carbon is most commonly obtained from coal deposits, although it usually must be processed into a form suitable for commercial use. Three naturally occurring allotropes of carbon are known to exist: amorphous, graphite and diamond. Amorphous carbon is formed when a material containing carbon is burned without enough oxygen for it to burn completely.

This black soot, also known as lampblack, gas black, channel black or carbon black, is used to make inks, paints and rubber products. It can also be pressed into shapes and is used to form the cores of most dry cell batteries, among other things. Graphite, one of the softest materials known, is a form of carbon that is primarily used as a lubricant. Although it does occur naturally, most commercial graphite is produced by treating petroleum coke, a black tar residue remaining after the refinement of crude oil, in an oxygen-free oven. Naturally occurring graphite occurs in two forms, alpha and beta. These two forms have identical physical properties but different crystal structures. All artificially produced graphite is of the alpha type. In addition to its use as a lubricant, graphite, in a form known as coke, is used in large amounts in the production of steel. Coke is made by heating soft coal in an oven without allowing oxygen to mix with it. Although commonly called lead , the black material used in pencils is actually graphite. Diamond, the third naturally occurring form of carbon, is one of the hardest substances known. Although naturally occurring diamond is typically used for jewelry, most commercial quality diamonds are artificially produced.

These small diamonds are made by squeezing graphite under high temperatures and pressures for several days or weeks and are primarily used to make things like diamond tipped saw blades. Although they posses very different physical properties, graphite and diamond differ only in their crystal structure. A fourth allotrope of carbon, known as white carbon, was produced in 1969. It is a transparent material that can split a single beam of light into two beams, a property known as birefringence. Very little is known about this form of carbon. Large molecules consisting only of carbon, known as buckminsterfullerenes, or buckyballs, have recently been discovered and are currently the subject of much scientific interest. A single buckyball consists of 60 or 70 carbon atoms (C60 or C70) linked together in a structure that looks like a soccer ball. They can trap other atoms within their framework, appear to be capable of withstanding great pressures and have magnetic and superconductive properties. Carbon-14, a radioactive isotope of carbon with a half-life of 5,730 years, is used to find the age of formerly living things through a process known as radiocarbon dating.

The theory behind carbon dating is fairly simple. Scientists know that a small amount of naturally occurring carbon is carbon-14. Although carbon-14 decays into nitrogen -14 through beta decay , the amount of carbon-14 in the environment remains constant because new carbon-14 is always being created in the upper atmosphere by cosmic rays. Living things tend to ingest materials that contain carbon, so the percentage of carbon-14 within living things is the same as the percentage of carbon-14 in the environment. Once an organism dies, it no longer ingests much of anything. The carbon-14 within that organism is no longer replaced and the percentage of carbon-14 begins to decrease as it decays. By measuring the percentage of carbon-14 in the remains of an organism, and by assuming that the natural abundance of carbon-14 has remained constant over time, scientists can estimate when that organism died. For example, if the concentration of carbon-14 in the remains of an organism is half of the natural concentration of carbon-14, a scientist would estimate that the organism died about 5,730 years ago, the half-life of carbon-14.

There are nearly ten million known carbon compounds and an entire branch of chemistry, known as organic chemistry, is devoted to their study. Many carbon compounds are essential for life as we know it. Some of the most common carbon compounds are: carbon dioxide (CO2), carbon monoxide (CO), carbon disulfide (CS2), chloroform (CHCl3), carbon tetrachloride (CCl4), methane (CH4), ethylene (C2H4), acetylene (C2H2), benzene (C6H6), ethyl alcohol (C2H5OH) and acetic acid (CH3COOH). Estimated Crustal Abundance: 2.00×102 milligrams per kilogram Estimated Oceanic Abundance: 2.8×101 milligrams per liter Number of Stable Isotopes: 2 ( View all isotope data ) Ionization Energy: 11.260 eV What is radiocarbon dating? | Earth | EarthSky What is radiocarbon dating?

By EarthSky in Earth | Human World | January 14, 2015 Unstable carbon-14 gradually decays to carbon-12 at a steady rate. The ratio of these carbon isotopes reveals the ages of some of Earth’s oldest inhabitants. Radiocarbon dating is a technique used by scientists to learn the ages of biological specimens – for example, wooden archaeological artifacts or ancient human remains – from the distant past. It can be used on objects as old as about 62,000 years. Follow the links below to learn more about radiocarbon dating. A special kind of radiocarbon dating: Bomb radiocarbon dating Although an element’s number of protons cannot change, the number of neutrons can vary slightly from each atom. Atoms of the same element that have different numbers of neutrons are called isotopes. Here’s an example using the simplest atom, hydrogen. Radiocarbon dating uses isotopes of the element carbon. Image via Mr. Gotney’s 8th grade science class. What is an isotope? To understand radiocarbon dating, you first have to understand the word isotope. An isotope is what scientists call two or more forms of the same element.

If you could peer at the atoms of two different isotopes, you would find equal numbers of protons but different numbers of neutrons in the atoms’ nucleus. So there’s a difference in the relative atomic masses of two isotopes. But they still have the same chemical properties. A carbon atom is a carbon atom is a carbon atom … Cosmic rays bombard Earth’s atmosphere, creating the unstable isotope carbon-14. This isotope lets scientists learn the ages of once-living specimens from long ago. Image via The Cosmic Story of Carbon-14 by Ethan Siegel , via Simon Swordy (U. Chicago), via NASA Radiocarbon dating uses carbon isotopes. Radiocarbon dating relies on the carbon isotopes carbon-14 and carbon-12. Scientists are looking for the ratio of those two isotopes in a sample. Most carbon on Earth exists as the very stable isotope carbon-12, with a very small amount as carbon-13. Carbon-14 is an unstable isotope of carbon that will eventually decay at a known rate to become carbon-12.

Cosmic rays – high energy particles from beyond the solar system – bombard Earth’s upper atmosphere continually, in the process creating the unstable carbon-14. Carbon-14 is considered a radioactive isotope of carbon. Because it’s unstable, carbon-14 will eventually decay back to carbon-12 isotopes. Because the cosmic ray bombardment is fairly constant, there’s a near-constant level of carbon-14 to carbon-12 ratio in Earth’s atmosphere. Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere. They have the same ratio of carbon-14 to carbon-12 as the atmosphere, and this same ratio is then carried up the food chain all the way to apex predators, like sharks. But when gas exchange is stopped, be it in a particular part of the body like in deposits on bones and teeth, or when the entire organism dies, the ratio of carbon-14 to carbon-12 begins to decrease. The unstable carbon-14 gradually decays to carbon-12 at a steady rate. And that’s the key to radiocarbon dating.

Scientists measure the ratio of carbon isotopes to be able to estimate how far back in time a biological sample was active or alive. Image via the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organizaiton This plot shows the level of carbon-14 in the atmosphere as measured in New Zealand (red) and Austria (green), representing the Northern and Southern Hemispheres, respectively. Aboveground nuclear testing almost doubled the amount of carbon-14 in the atmosphere. That’s why aboveground nuclear testing was banned. The black arrow shows when the Partial Test Ban Treaty was enacted that banned aboveground nuclear tests. Image via Hokanomono via Wikimedia Commons. A special kind of radiocarbon dating: Bomb radiocarbon dating. As we mentioned above, the carbon-14 to carbon-12 ratio in the atmosphere remains nearly constant. It’s not absolutely constant due to several variables that affect the levels of cosmic rays reaching the atmosphere, such as the fluctuating strength of the Earth’s magnetic field, solar cycles that influence the amount of cosmic rays entering the solar system, climatic changes, and human activities.

Among the significant events that caused a temporary but significant spike in the atmospheric carbon-14 to carbon-12 ratio were above-ground nuclear test detonations in the two decades following World War II. Bomb radiocarbon dating is a term for radiocarbon dating based on timestamps left by above-ground nuclear explosions, and it is especially useful for putting an absolute age on organisms that lived through those events. In The Cosmic Story of Carbon-14 Ethan Siegel writes: The only major fluctuation [in carbon-14] we know of occurred when we began detonating nuclear weapons in the open air, back in the mid-20th Century. If you ever wondered why nuclear tests are now performed underground, this is why. Most radiocarbon dating today is done using an accelerator mass spectrometer , an instrument that directly counts the numbers of carbon 14 and carbon12 in a sample. A detailed description of radiocarbon dating is available at the Wikipedia radiocarbon dating web page . Bottom line: Radiocarbon dating is a technique used by scientists to learn the ages of biological specimens – for example, wooden archaeological artifacts or ancient human remains – from the distant past.

It can be used on objects as old as about 62,000 years. Follow the links in this post to learn more about radiocarbon dating. carbon-14 | isotope | Britannica.com Carbon-14 THIS IS A DIRECTORY PAGE. Britannica does not currently have an article on this topic. Learn about this topic in these articles: in nuclear medicine Different isotopes tend to concentrate in particular organs: for example, iodine-131 settles in the thyroid gland and can reveal a variety of defects in thyroid functioning. Another isotope, carbon-14, is useful in studying abnormalities of metabolism that underlie diabetes, gout, anemia, and acromegaly. Various scanning devices and techniques have been developed, including tomography... in photosynthesis: Elucidation of the carbon pathway Radioactive isotopes of carbon ( 14C) and phosphorus ( 32P) have been valuable in identifying the intermediate compounds formed during carbon assimilation. A photosynthesizing plant does not strongly discriminate between the most abundant natural carbon isotope ( 12C) and 14C. During photosynthesis in the presence of 14CO 2, the...

in dating (geochronology): Technical advances ...by counting the number of disintegrations per minute ( i.e., emission activity). The rate is related to the number of such atoms present through the half-life. For example, a certain amount of carbon-14 ( 14C) is present in all biological components at the Earth’s surface. This radioactive carbon is continually formed when nitrogen atoms of the upper atmosphere collide with... in dating (geochronology): Carbon-14 dating and other cosmogenic methods The discovery of natural carbon-14 by American chemist Willard Libby of the United States began with his recognition that a process that had produced radiocarbon in the laboratory was also going on in Earth’s upper atmosphere—namely, the bombardment of nitrogen by free neutrons. Newly created carbon-14 atoms were presumed to react with atmospheric oxygen to form carbon dioxide... in archaeology: Dating ...prehistoric archaeology occurred in 1948, when Willard F. Libby, at the University of Chicago, developed the process of radioactive carbon dating.

In this method, the activity of radioactive carbon ( carbon-14) present in bones, wood, or ash found in archaeological sites is measured. Because the rate at which this activity decreases in time is known, the approximate age of the material can be... Facts About Carbon Facts About Carbon By Stephanie Pappas, Live Science Contributor | August 9, 2014 06:32pm ET MORE Credit: general-fmv , Andrei Marincas | Shutterstock Carbon is an incredible element. Arrange carbon atoms in one way, and they become soft, pliable graphite. Re-jigger the arrangement, and — presto! — the atoms form diamond, one of the hardest materials in the world. Carbon is also the key ingredient for most life on Earth; the pigment that made the first tattoos; and the basis for technological marvels such as graphene, which is a material stronger than steel and more flexible than rubber.

[See Periodic Table of the Elements ] Carbon occurs naturally as carbon-12, which makes up almost 99 percent of the carbon in the universe; carbon-13, which makes up about 1 percent; and carbon-14, which makes up a minuscule amount of overall carbon but is very important in dating organic objects. Just the facts Atomic Number (number of protons in the nucleus): 6 Atomic Symbol (on the Periodic Table of Elements): C Atomic Weight (average mass of the atom): 12.0107 Density: 2.2670 grams per cubic centimeter Phase at Room Temperature: Solid Melting Point: 6,422 degrees Fahrenheit (3,550 degrees C) Boiling Point: 6,872 F (3,800 C) (sublimation) Number of isotopes: 15 total; two stable isotopes, which are atoms of the same element with a different number of neutrons.

Most common isotopes: carbon-12 (6 protons, 6 neutrons and 6 electrons) and carbon-13 (6 protons, 7 neutrons and 6 electrons) Carbon: From stars to life As the sixth-most abundant element in the universe, carbon forms in the belly of stars in a reaction called the triple-alpha process, according to the Swinburne Center for Astrophysics and Supercomputing. In older stars that have burned most of their hydrogen , leftover helium accumulates. Each helium nucleus has two protons and two neutrons. Under very hot temperatures — greater than 100,000,000 Kelvin (179,999,540.6 F) — the helium nuclei begin to fuse, first as pairs into unstable 4-proton beryllium nuclei, and eventually, as enough beryllium nuclei blink into existence, into a beryllium plus a helium. The end result: Atoms with six protons and six neutrons — carbon.

While scientists sometimes conceptualize electrons spinning around an atom's nucleus in a defined shell, they actually fly around the nucleus at various distances; this view of the carbon atom can be seen here in two electron cloud figures (bottom), showing the electrons in a single blob (the so-called s-orbital) and in a two-lobed blob or cloud (the p-orbital). Credit: Physical Review B, DOI: 10.1103/PhysRevB.80.165404 Carbon is a pattern maker. It can link to itself, forming long, resilient chains called polymers. It can also bond with up to four other atoms because of its electron arrangement. Atoms are arranged as a nucleus surrounded by an electron cloud, with electrons zinging around at different distances from the nucleus. Chemists conceive of these distances as shells, and define the properties of atoms by what is in each shell, according to the University of California, Davis . Carbon has two electron shells, with the first holding two electrons and the second holding four out of a possible eight spaces. When atoms bond, they share electrons in their outermost shell. Carbon has four empty spaces in its outer shell, enabling it to bond to four other atoms.

(It can also bond stably to fewer atoms by forming double and triple bonds.) In other words, carbon has options. And it uses them: Nearly 10 million carbon compounds have been discovered, and scientists estimate that carbon is the keystone for 95 percent of known compounds, according to the website Chemistry Explained. Carbon's incredible ability to bond with many other elements is a major reason that it is crucial to almost all life. Carbon's discovery is lost to history. The element was known to prehistoric humans in the form of charcoal. Carbon as coal is still a major source of fuel worldwide, providing about 30 percent of energy worldwide, according to the World Coal Association. Coal is also a key component in steel production, while graphite, another form of carbon, is a common industrial lubricant. Carbon-14 is a radioactive isotope of carbon used by archaeologists to date objects and remains. Carbon-14 is naturally occurring in the atmosphere. Plants take it up in respiration, in which they convert sugars made during photosynthesis back into energy that they use to grow and maintain other processes, according to Colorado State University . Animals incorporate carbon-14 into their bodies by eating plants or other plant-eating animals.

Carbon-14 has a half-life of 5,730 years, meaning that after that time, half of the carbon-14 in a sample decays away, according to the University of Arizona . Because organisms stop taking in carbon-14 after death, scientists can use carbon-14's half-life as a sort of clock to measure how long it has been since the organism died. This method works on once-living organisms, including objects made of wood or other plant material. Who knew? Carbon gets its name from the Latin word carbo, which means "coal." Diamonds and graphite are among the hardest and softest natural materials known, respectively. The only difference between the two is their crystal structure. Carbon makes up 0.032 percent of the Earth's lithosphere (crust and outer mantle) by weight, according to the Encyclopedia of Earth.

A rough estimate of the weight of the lithosphere by La Salle University geologist David Smith is 300,000,000,000,000,000,000,000 (or 3*10^23) pounds, making the approximate weight of carbon in the lithosphere 10,560,000,000,000,000,000,000 (or 1.056*10^22) pounds. Carbon dioxide (a carbon atom plus two oxygen atoms) makes up about 0.04 percent of Earth's atmosphere, according to the National Oceanic & Atmospheric Administration (NOAA) — an increase over pre-industrial times, because of the burning of fossil fuels. Carbon monoxide (a carbon atom plus one oxygen atom) is an odorless gas produced from the burning of fossil fuels. Carbon monoxide kills by binding to hemoglobin, the oxygen-carrying compound in the blood.

Carbon monoxide bonds to hemoglobin 210 times more strongly than oxygen binds to hemoglobin, effectively crowding out oxygen and suffocating the tissues, according to a 2001 paper in the Journal of the Royal Society of Medicine . Diamond, the flashiest version of carbon, is formed under great pressure deep in the Earth's crust. The largest gem-quality diamond ever found was the Cullinan diamond, which was discovered in 1905, according to the Royal Collection Trust . The uncut diamond was 3,106.75 carats. The largest gem cut from the stone, at 530.2 carats, is one of the Crown Jewels of the United Kingdom and is known as the Great Star of Africa. The tattoos of Ötzi the Iceman , a 5,300-year-old corpse found frozen in the Alps, were inked from carbon, according to a 2009 study in the Journal of Archaeological Science. Small incisions in the skin were made, and charcoal rubbed in, perhaps as part of an acupuncture treatment. Ongoing research Carbon is a long-studied element, but that doesn't mean there isn't more to discover.

In fact, the same element that our prehistoric ancestors burned as charcoal may be the key to next-generation tech materials. In 1985, Rick Smalley and Robert Curl of Rice University in Texas and their colleagues discovered a new form of carbon. By vaporizing graphite with lasers, the scientists created a mysterious new molecule made of pure carbon, according to the American Chemical Society . This molecule turned out to be a soccer-ball-shaped sphere made of 60 carbon atoms. The research team named their discovery the buckminsterfullerene after an architect who designed geodesic domes. The molecule is now more commonly known as the "buckyball." The researchers who discovered it won a Nobel Prize in Chemistry in 1996. Buckyballs have been found to inhibit the spread of HIV, according to a study published in 2009 in the Journal of Chemical Information and Modeling ; medical researchers are working to attach drugs, molecule-by-molecule, to buckyballs in order to deliver medicine directly to sites of infection or tumors in the body; this includes research by Columbia University , Rice University and others.

Since then, other new, pure carbon molecules — called fullerenes — have been discovered, including elliptical-shaped "buckyeggs" and carbon nanotubes with amazing conductive properties. Carbon chemistry is still hot enough to capture Nobel Prizes: In 2010, researchers from Japan and the United States won one for figuring out how to link carbon atoms together using palladium atoms, a method that enables the manufacture of large, complex carbon molecules, according to the Nobel Foundation. Scientists and engineers are working with these carbon nanomaterials to build materials straight out of science-fiction. A 2010 paper in the journal Nano Letters reports the invention of flexible, conductive textiles dipped in a carbon nanotube "ink" that could be used to store energy, perhaps paving the way for wearable batteries, solar cells and other electronics. Perhaps one of the hottest areas in carbon research today, however, involves the "miracle material" graphene. Graphene is a sheet of carbon only one atom thick. It's the strongest material known while still being ultralight and flexible. And it conducts electricity better than copper.

Mass-producing graphene is a challenge, though researchers in April 2014 reported that they could make large amounts using nothing but a kitchen blender . If scientists can figure out how to make lots of graphene easily, the material could become huge in tech. Imagine flexible, unbreakable gadgets that also happen to be paper-thin. Carbon has come a long way from charcoal and diamonds, indeed. Follow Stephanie Pappas on Twitter and Google+ . Follow us @livescience , Facebook & Google+ . Learn more about carbon: Carbon Dating Background Background Information _____________________________ Carbon dating is used to determine the age of biological artifacts up to 50,000 years old. This technique is widely used on recent artifacts, but teachers should note that this technique will not work on older fossils (like those of the dinosaurs which are over 65 million years old). This technique is not restricted to bones; it can also be used on cloth, wood and plant fibers. Carbon-14 dating has been used successfully on the Dead Sea Scrolls, Minoan ruins and tombs of the pharohs among other things. What is Carbon-14? Carbon-14 is a radioactive isotope of carbon.

Its has a half-life of about 5,730 years. The short half-life of carbon-14 means its cannot be used to date extremely old fossils. Levels of carbon-14 become difficult to measure and compare after about 50,000 years (between 8 and 9 half lives; where 1% of the original carbon-14 remains undecayed). How is Carbon-14 formed? Carbon-14 is created from nitrogen-14 in the upper atmosphere of the earth. Radiation from the sun collides with atoms in the atmosphere. These collisions create secondary cosmic rays in the form of energentic neutrons. When these neutrons collide with nitrogen-14 in the atmosphere carbon-14 can be created. Nitrogen normally occurs in a seven proton, seven nuetron, nitrogen-14 state. When it collides with an energetic neutron it becomes carbon-14, with six protons and eight neutrons and gives off a hydrogen atom with one proton and zero neutrons. How is Carbon-14 used to date artifacts? Most of the carbon on Earth exists as carbon-12.

Carbon-14 is an isotope of carbon, which exists only is small amounts in the environment (1 in one trillion carbon atoms is carbon-14). The ratio of carbon-14 to carbon-12 in the atmosphere and on earth is nearly constant, although there has been some change in carbon-14 concentration over the last 10,000 years. Carbon-14 formed in the atmosphere can combine with oxygen to form carbon dioxide (CO2). This carbon-14 labeled carbon dioxide is taken up by plants in their normal process of photosynthesis. Animals and people that eat these plants take the carbon-14 into their bodies as well. Carbon-14 in the bodies of animals and plants is constantly decaying. However, the decaying carbon-14 is constantly being replaced as the plant or animal consumes more carbon-14 from the air or through its food. At any given moment all living plants and animals have approximately the same percentage of carbon-14 in their bodies. When a plant or animal dies it stops bringing in new carbon-14. However, the carbon-14 already in the organism's body continues to decay at a constant rate.

Therefore, the amount of carbon-14 in an artifact decreases at a predictable rate while the amount of carbon-12 remains constant. By comparing the ratio of carbon-14 to carbon-12 in an artifact to the ratio of carbon-14 to carbon-12 in living organisms scientists can determine the age of an artifact. So how do I use my carbon-14 data? A formula used in carbon dating is: t = [ln (Nf/No) / (-0.693)] * t1/2 where ln (Nf/No) = the natural logarithm of the percent carbon-14 in the sample compared to the percent carbon-14 in living tissue, and t1/2 = the half-life of carbon-14 = 5,700 years. If you wanted to date a fossil, first you would determine the percent carbon-14 it contained compared to a living sample. Imagine your sample contained 20% of the carbon-14 found in a living plant leaf.

Then, t = [ln (0.2) / (-0.693)] * 5,700 years t = [(-1.609) / (-0.693)] * 5,700 years t = [2.322] * 5,700 years Will Carbon-14 dating work on all artifacts? No. There are a few categories of artifacts that cannot be dated using carbon-14. First, carbon-14 cannot be used to date biological artifacts of organisms that did not get thier carbon dioxide from the air. This rules out carbon dating for most aquatic organisms, because they often obtain at least some of their carbon from dissolved carbonate rock. The age of the carbon in the rock is different from that of the carbon in the air and makes carbon dating data for those organisms inaccurate under the assumptions normally used for carbon dating. This restriction extends to animals that consume seafood in their diets, as well. Carbon dating also cannot be used on artifacts over about 50,000 years old.

These artifacts have gone through many carbon-14 half-lives and the amount of carbon-14 remaining in them is miniscule and very difficult to detect. Carbon dating cannot be used on most fossils, not only because they are almost always too old, but also because they rarely contain the original carbon of the organism. Also, many fossils are contaminated with carbon from the environment during collection or preservation proceedures. How do we know Carbon-14 dating is accurate? Scientists check the accuracy of carbon dating by comparing carbon dating data to data from other dating methods. Other methods scientists use include counting rock layers and tree rings. When scientists first began to compare carbon dating data to data from tree rings, they found carbon dating provided "too-young" estimates of artifact age. Scientists now realize that production of carbon-14 has not been constant over the last 10,000 years, but has changed as the radiation from the sun has changed. Carbon dates reported in the 1950s and 1960s should be questioned, because those studies were conducted before carbon dating was calibrated by comparision with other dating methods.

Nuclear tests, nuclear reactors and the use of nuclear weapons have also changed the composition of radioisotopes in the air over the last few decades. This human nuclear activity will make precise dating of fossils from our lifetime very difficult due to contamination of the normal radioisotope composition of the earth with addition artificially produced radioactive atoms. How do scientists date older fossils? Although the half-life of carbon-14 makes it unreliable for dating fossils over about 50,000 years old, there are other isotopes scientists use to date older artifacts. These isotopes have longer half-lives and so are found in greater abundance in older fossils.

Some of these other isotopes include: Potassium-40 found in your body at all times; half-life = 1.3 billion years Uranium-235; half-life = 704 million years Uranium-238; half-life = 4.5 billion years Thorium-232; half-life = 14 billion years Rubidium-87; half-life = 49 billion years BioMath: Carbon Dating Carbon Dating Carbon dating to determine the age of fossil remains In this section we will explore the use of carbon dating to determine the age of fossil remains. Carbon is a key element in biologically important molecules. During the lifetime of an organism, carbon is brought into the cell from the environment in the form of either carbon dioxide or carbon-based food molecules such as glucose; then used to build biologically important molecules such as sugars, proteins, fats, and nucleic acids. These molecules are subsequently incorporated into the cells and tissues that make up living things. Therefore, organisms from a single-celled bacteria to the largest of the dinosaurs leave behind carbon-based remains.

Carbon dating is based upon the decay of 14C, a radioactive isotope of carbon with a relatively long half-life (5700 years). While 12C is the most abundant carbon isotope, there is a close to constant ratio of 12C to 14C in the environment, and hence in the molecules, cells, and tissues of living organisms. This constant ratio is maintained until the death of an organism, when 14C stops being replenished. At this point, the overall amount of 14C in the organism begins to decay exponentially. Therefore, by knowing the amount of 14C in fossil remains, you can determine how long ago an organism died by examining the departure of the observed 12C to 14C ratio from the expected ratio for a living organism. Decay of radioactive isotopes Radioactive isotopes, such as 14C, decay exponentially. The half-life of an isotope is defined as the amount of time it takes for there to be half the initial amount of the radioactive isotope present. For example, suppose you have N0 grams of a radioactive isotope that has a half-life of t* years.

Then we know that after one half-life (or t* years later), you will have grams of that isotope.

Question: Which isotope of Carbon is used in 'Carbon Dating'?
Answer: Carbon 14